A commenter made a good point regarding something I said in one of my follow-up comments in the thread after my rant on intermediate fossils that I thought I would move up here to respond to.
Oldfart: While you are at it, explain “primitive” and “advanced” traits. Since it is also often said that later is more advanced than earlier assuming some kind of “direction”.
You’re right I should clarify this.
The terms “primitive” and “advanced” in evolutionary biology are relative rather than absolute terms. “Primitive” simply means more like the original or less modified from previous iterations, likewise “advanced” means less like the original or more modified. A character being primitive does not mean that it is necessarily inferior or backwards and a character being advanced does not make it superior in any absolute sense.
For example, humans are primitive with regards to our hands and feet bearing the typical tetrapod compliment of five digits each (very early tetrapods had more toes but that is another story), whereas horses are are advanced in having modified both fore and hind feet down to a single digit; digit #3 which is homologous to our middle finger/toe.
Our hands serve us quite well despite their primitiveness and while the advanced hooves of equids are excellent for use in galloping around with, they don’t exactly allow horses a precision grip.